The present invention relates to a laser radar ("LADAR") seeker and guidance system adapted to scan a target area with laser energy, detect the reflected laser energy, and compute range and intensity values, permitting the processing of guidance and control signals for the missile as it approaches the target.
Known laser radar systems have used an apertured mirror in various applications. For example, in U.S. Pat. No. 4,042,822, an expanded beam strikes an apertured mirror and a portion of the light beam passes through the aperture to strike a photodetector. However, such a system mixes return energy with laser beam energy passed through the aperture to provide heterodyne detection of the received target signals. Thus, there remains a need for a laser radar system that includes a turning mirror with an off-center aperture to reflect return light onto a photodetector. This aperture could consist of a mirror with a hole in it or conversely a small mirror on a clear plate. Such a system should advantageously eliminate the need for certain mirrors and lenses, thus simplifying construction and therefore lowering costs. This use maximizes the effective throughput of the LADAR even when central obscuration is present and/or unpolarized beams are used. The aperture is off-center since a secondary mirror located forwardly of a primary mirror is centrally located. The losses on the output beams are minimal and, on the return beams, are limited to the ratio of the output beam area to the return beam area.